Isomerization of carane



rsor/mnrZArroN on CARANE Alfred L. Rnmmelsbnrg, Chadds Ford, Pa., assignor to Hercules Powder Company, Wilmington, Del., 21 corporation of Delaware No Drawing. Application January 27, 1955 Serial No. 561,923

3 Claims. (Cl. 260-666) The present invention relates to a process for the isomerization of carane to a product rich in menthenes.

,The hydrocarbon carane is easily prepared by hydrogenation of carene. The latter compound has never been in abundant supply but in recent years investigation of certain western pine stumps as a source for rosin and terpenes has disclosed that carene is a major constituent of the extracts of such stumps. This finding has thus made available a potentially rich source of carene and, indirectly, of carane.

It is known that menthylphenol, which is a valuable ingredient of certain synthetic resin compositions, can be produced readily by condensing a menthene with phenol. However, in the past the relatively high cost of menthenes has been a deterrent to the production and sale of menthylphenol in quantity. It is accordingly an object of the present invention to provide a method whereby carane can be isomerized to a product rich in menthenes thus furnishing an important step in an inexpensive route for the production of menthylphenol.

In accordance with the invention there is provided a process which comprises contacting carane at a temperature of from about to 200 C. with a strong acid that is nonoxidizing at the stated temperature in the presence of water in an amount suflicient to dilute said acid to the pointthat isomerization of carane to menthenes takes place without substantial polymerization.

It was not to be expected that carane could be isomerized under the aforesaid conditions in view of indications in the literature that such closely related hydrocarbons as pinane and thujane are unaffected by dilute solutions of strong acids even at relatively high temperatures. It is known, of course, that carane, as well as pinane and thujane, can be polymerized by treatment with concentrated solutions of strong acids. This invention is distinguished from these known polymerization reactions by the use of more dilute solutions of acid which makes possible an entirely different result.

In order to illustrate the invention in a more specific manner, the following examples are presented. Parts and percentages are by weight unless otherwise specified.

Example I Into a reaction vessel there were placed 200 parts of substantially pure carane (bromine number 0.5-1.3) and 200 parts of aqueous 50% sulfuric acid. This mixture was heated with continuous agitation over a period of 20 minutes to the reflux temperature (approximately 105 C.) and this temperature was maintained over a period of 7 hours. At various times during the course of the reaction, samples of the reaction mixture were withdrawn, and the oil layer separating from each sample was washed with water and dried. Bromine numbers of the samples were taken to indicate the course of the ited rates Patent C) reaction. The samples were also examined by infrared analysis. The results are tabulated below:

Time (Hrs) Bromine Number I. R. Analysis (Approximate) -90% carane, 5% or less 3-menthene, 1-2% 8, Q-menthenes.

N o Apparent Difference.

65-70% carane, 10% 3-menthene, 34% 8,9-

menthenes.

60-60% earane, 20% 3-menthene, 56% 8,9-

menthenes.

It is apparent that the reaction proceeded with fair rapidity resulting in a product containing an appreciable quantiyt of menthenes which can, if desired, be isolated by conventional techniques.

Example 11 The procedure of Example I was repeated using parts of aqueous 50% sulfuric acid instead of 200 parts. The bromine numbers of samples taken at various times are tabulated below:

Bromine number Example 111 The procedure of Example I was repeated using parts of carane and 350 parts of aqueous 50% sulfuric acid. The bromine numbers of samples taken at various intervals are as follows:

Time (hrs): Bromine number 0.5 103 Example IV In a reaction vessel there were placed 350 parts of carane and 175 parts of aqueous 67% sulfuric acid. This mixture was heated with continuous agitation to a temperature of 45 C. and this temperature was maintained for 6 hours. The bromine numbers of samples taken from time to time are given below.

Time (hrs.): Bromine number 0.5 11

The slowness of this reaction in comparison with preceding reactions is attributable to the lower temperature employed.

Example V Into a reaction vessel there were placed 175' parts of carane and 350 parts of aqueous 25% sulfuric acid. This mixture was heated with continuous agitation over a period of about 20 minutes to the reflux temperature (approximately 105 C.) and this temperature was maintained for 7 hours. The bromine numbers. ,of samples taken at various intervals were asfollows:

Time (hrs): 7

Example, =VI

Into a reaction vessel there ere placed 300 parts of carane and 600 parts of aqueous 65% phosphoric acid. The mixture was heated to reflux (approximately 103" C.) for 5 hours with continuous agitation an3p le taken as previously described, showed bromine numbers as follows: 7 l h l l Time (h b om ne number Example VII 7 The .pI-ocedure o E ampl was .fsll bst tutmg 600 parts of aqueous 20% hydrochloric phosphoric acid of the prior example.

The sideline numbers of samples taken during the reaction were-as follows:

Time (hrs.): Bromine number 1.0 50 3.0 77 5.0 92

Bromine I. R. Analysis (Approximate) Number H Garage, 1. %..3-n e e ze 0% 8,9-menthenes 2.. 130 1015% carane, 35.-4Q% Muenthene, 8- l0% 8,9-menthenes. i 3 131 5-10% carane, 40-50% '3 H18Ilth9l18, -79% 1 Unidentifiable menthenes were alsopresent.

As stated before, the process .of the -invention.comprises contacting carane at a temperature from about to 200 C. with a strong acid that is nonoxidizing at the reaction temperature in the presence of suflicient water to dilute said acid to thepointthat isomerization of carane to menthenes takes place without substantial polymerization.

The acids which ,are operable in the invention-are those inorganic and organicacids-whichare nonoxidizing at the reaction temperature and which-are at least afs strong as acetic acid. Thus, nitricacid is excluded because of its oxidizing properties but other mineral acids such as sulfuric acid, .phosphoricacid, hydrochloric-acid, hydrobromic acid, .thiophosphoric acid, .and like Linorganic acids are included. Similar1y,.organic..acids "such as acetic acid,.oxalic acid, chloroaceticacid, dichloroacetic acid, trichloroacetic acid, maleic acid, p-toluene u n acid, h y u n a id, an t e o san ca id that can'be classified as strong acids within the-meaning '4 of the invention are operable. Of all the acids that are u tu ic aci is pre e ed by reason of t e rapidity of reaction obtained therewith coupled with its relatively low cost.

Since the object of the invention is to elfect isomerization without substantial polymerization, the use of strong acids in concentrated form is to be avoided because under such conditions the ultimate reaction that occurs is polymerization. Accordingly, water must be employed as a diluent, the exact amount of water in any given instance depending upon the strength of the acid that is to be used. The stronger the acid is, the larger the quantity of water in relation to the acid that will be required. als pssuited? a id a .e s pla i o ri at qn withq polymerization can be brought about if sufficient water is used to dilute the acid to at least about 75% concentration. The invention, however, .is not limited to any fixed minimum concentration because any finite concentration of acid can promote the desired reaction although in the case of sulfuric acid, for example, a concentration below about 10% results in a slow reaction.

T e same ssshins w hres sc 01116 sc sssn r ti of id .area nli ab 10 t e other acids msst s P F. bearing in mind the fact that the weaker the acid, the mo e assnt stsd 1 Thus, f r e m a eti acid n ay be ernployed in a concentration as high as about 96% .whereas phosphoric acid must be diluted to about the same e n s l sr a dm his, plapati gn, those skilled in the art will readily understand he sun... can be utilized.

-T l he,quantity .of acid .in relation to the quantity of cara ne can-be widely varied with some .infiuencapf amuse, t e a d of h reactidn; n, ge th greater the quantity of acid in relation to .carane, the more rapid the reaction will be. As a practical matter a it 1 s .desi rablelthat the weight of acid plus the weightof water notexceed about 10 times the weight of cares Qnthe opposite extreme, it is desirable fromthe practical stasd si t at the Weight o m P111S e h o water be not lessthan about2% by weight ofthe carane.

' It is -.p re ferr ed that the combined weight of acid and waterilbefrorn about 0.5 .to 3 times the weight of carane.

The reaction is desirably carried out by agitating a mixture of carane, water, and acid at a temperature within the range previously stated. In accordance with the general ruleslof chemistrygthe higher the reaction temperature, the greater will .be the rapidity of the reactipn. Howev er, for practical purposes "it is desirable to avoid (the. use of pressurized equipment so that a temperature, no higherth'an the atmospheric reflex temperatureof the reaction mixture is preferred. Withfthe can be removed by washing-with water.

aforesaid considerations in mind, a preferred range of re action ternperatures is from about 20 to C.

Thetime of reaction isquite variable since it depends upon the nun'rerousfactors discussed above. Under the prfiffil'rfid Qudi 'ons, however, it can be said that the reaction l ord narily require from about 1 to 15 hours for substantial completion. At the termination, either eaqtian i t act dm i ma s arat by a simP de antati o 'nto an oil layer and a water layer. The

oilla yer, of ourse,'c0ntai ns the desired reaction and traces of acid which may contaminate this product In the usual qa se,.the product will comprise amixture of unreacted carane, 3;:rnenthene, and other menthenes. l fthe i nenthens -s s.s s d in ru et rmi they may be par t from .thereaction mixture 'by jractional distillationfor other conventional .separatory techniques.

' What I c l mend desire to.protect byLetters Patent isi 1.. The .process for -,the ,isomerization of .carane ,to menthenesbwhich ;comprises contacting carane at a temperaturepf vfromabo ut 20 to 110, C. with an aqueous aQ 1 =td;fi. m the sm s st n c que u s furic-.acid of .a concentration no greater than 75%,

r xis atemaximsm o t ns 9 s d liieh aqueous phosphoric acid of a concentration no greater thenes which comprises contacting carane at a temperathan 75%, aqueous hydrochloric acid of a concentration ture of from about 20 to 110 C. With aqueous phosno greater than 20%, aqueous oxalic acid of a concenphoric acid of a concentration no greater than 75%. tration no greater than 50%, and aqueous acetic acid of a concentration no greater than 96%. 5 References Cited in the file Of this patent 2. The process for the isomerization of carane to UNITED STATES PATENTS menthenes WhlCh comprises contacting carane at a tem- 2,097,744 Sheflield NOV 2 1937 perature of from about 20 to 110 C. with aqueous sulfuric acid of a concentration no greater than 75%.

3. The process for the isomerization of carane to men- 10 2,399,741 Ipatiefi et a1. May 7, 1946 

1. THE PROCESS FOR THE ISOMERIZATION OF CARANE TO MENTHENES WHICH COMPRISES CONTACTING CARANE AT A TEMPERATURE OF FROM ABOUT 20 TO 110*C. WITH AN AQUEOUS ACID SELECTED FROM THE GROUP CONSISTING OF AQUEOUS SULFURIC ACID OF A CONCENTRATION NO GREATER THAN 75%, AQUEOUS PHOSPHORIC ACID OF A CONCENTRATION NO GREATER THAN 75%, AQUEOUS HYDROCHLORIC ACID OF A CONCENTRATION NO GREATER THAN 20%, AQUEOUS OXALIC ACID OF A CONCENTRATION NO GREATER THAN 50%, AND AQUEOUS ACETIC ACID OF A CONCENTRATION NO GREATER THAN 96%. 